Find source locations even when clojure doesn't report them.

Search on emacs side when locations are not reported by clojure (pretty much for all interactive evaluations). Currently the regexp searches for "(def.*"  and works as expected for most common top level declarations.  

For inner declarations (letfn) a more extensive patch would be needed because the stored var for function `ns/foo/fn` is `ns/foo` and I don't see how to get info for inner function with existing middleware. 

This patch addresses #631.
> for interactive eval and your code pretty much does nothing as buffer gets set to nil

In all my experiments "ns" had a file metadata. I assume it's because my first evaluation was always with <kbd>C-c C-k</kbd>. Thanks for making it more general. I hope all of these regexp based workarounds are cleaned sooner than later.